The present invention relates to a chucking apparatus for holding a tool.
A technique for exhibiting a strong cutting force to a tool has been proposed in Japanese Utility Model Examined Publication No. Hei 3-29056 (hereinafter referred to as the prior art).
In the prior art, semicylindrical concave and convex portions which are engaged with each other are formed in a proximal end face of a tool and a contact portion of a chucking apparatus body with which the proximal end face of the tool is brought into contact (in which upright surfaces of the semicylindrical concave and convex portions to face each other are perpendicular to the respective end faces). The concave and convex engagement of the concave and convex portions ensures a good transmission of a rotational torque to thereby exhibit a strong cutting force.
However, the prior art technique suffers from the following outstanding problems.
Namely, it is sure that the prior art may ensure the good transmission of the rotational torque to the tool and exhibits a strong cutting force but there is an outstanding problem relating to the enhancement of the holding force for the tool in the axial direction.
More specifically,
i) in FIGS. 1 and 2, in case of boring a penetration hole 32 with a tool (drill 31), because a force for forcing the drill 31 apart from a chucking apparatus 34 is generated when the drill 31 has penetrated through a workpiece 33 to be worked, there is a fear that the drill 31 would be pulled away from the chucking apparatus 34.
This will be explained in detail with reference to FIGS. 1 and 2.
The drill 31 is composed of two teeth and loci of the teeth are spiral during the operation.
The moment at which the drill 31 has passed through the workpiece 32 is shown in FIG. 2 as viewed from the penetration side.
Since cutting tooth portions 31' of the drill 31 are rotationally moving in a spiral manner, the hatched portions in FIG. 2 have not yet been cut. However, since all the tip ends of the cutting tooth portions 31' of the drill 31 have passed through the workpiece, side wall portions 31" of the drill 31 are used to cut the hatched portions in FIG. 2.
Since the side wall portions 31" of the drill 31 have a twist angle, a tension force for drawing the drill per se is generated by the twist angle during the working operation of the hatched portions.
ii) There is a fear that the drill would be pulled apart from the chucking apparatus by the frictional force when the deep boring has been effected with the drill and the latter is pulled apart from the deep hole.
iii) In case of a drill apparatus in which the chuck apparatus is vibrated in the axial direction under the condition that the drill is held and a hole is formed while imparting a shock to the drill, or in case of another drill apparatus in which a hole is formed by striking a proximal end of a drill held by claw members with an air hammer (the two types of the drill apparatus will hereinafter be referred to as a striking drill apparatus), since a force is applied to the drill in the axial direction (toward the tip end of the drill), there is a fear that the drill would be pulled apart. In particular in the case where a friction is remarkable between the claw members for holding the drill and the tool, this phenomenon is remarkable.